Interleukin 2 (IL2) or T cell growth factors (TCGF) is a T cell-derived glycoprotein hormone which stimulates the proliferation of activated T lymphocytes, mediated through its binding to specific cell surface receptors. Levels of available IL2 determine, therefore, to a large extent, the magnitude of T cell-dependent humoral and cellular immune responses. IL2 was shown to correct some immunodeficiencies and induce or augment various effector cell functions in experimental systems, and defects in its production and/or responsiveness have been identified in various diseases. Despite some significant recent advances in IL2 studies, i.e., identification of IL2-producing continuous T cell lines, development of purification procedures and molecular cloning of the human IL2 gene, the structure-function relationship and physiological role of IL2 and its immunotherapeutic potential are far from being clear. In addition, quantitative IL2 immunoassays which would supplement or replace the current bioassay have not been reported. Thus, the objective of this proposal is to develop reliable quantitative assays for measuring IL2 levels in biological fluids, and enumerating IL2-producing/containing cells in health and disease, and to gain an understanding of the structure-function relationship and physiological role of IL2. To achieve this objective, we will: 1) Purity and isolate natural or recombinant human IL2 and prepare enzymatically-digested or chemically-synthesized IL2 peptides, based on the known amino acid sequence of human IL2; 2) Prepare polyclonal or monoclonal antibodies against IL2 peptides, followed by immunochemical and functional characterization of such antibodies; 3) Use such antibodies, as well as antibodies against natural or recombinant IL2, to develop quantitative IL2 immunoassays, or procedures to enumerate IL2-containing/producing cells; 4) Apply the above assays to the measurement of IL2 levels in culture or body fluids, and the enumeration of IL2-positive cells in suspensions or tissue sections, both in normal donors and in patients with autoimmune (SLE, rheumatoid arthritis, and Sjogren's) or malignant disease; 5) Use IL2 peptides or analogs and antibodies made against different forms of human IL2 to elucidate the structure-function relationship of this lymphokine and identify its active site(s). These studies are likely to result in a better understanding of the structure-function relationship of IL2, its physiological role in the immune system, and the significance of IL2 defects, as well as its immunotherapeutic potential, in various diseases.